1. Field of the Invention
The invention relates to a heterogeneous metathesis catalyst comprising a support, a metal compound the metal of which has been chosen from the group formed by tungsten, rhenium and molybdenum, and a promoter. The invention also relates to a catalytic process for the metathesis of olefins.
2. Description of Related Art
A metathesis is a reaction in which olefins are catalytically converted into other olefins having a different molecular weight through exchange between olefin molecules of groups situated at the double bond of the olefin molecule. An example is the conversion, through metathesis, of 2-pentene into 2-butene and 3-hexene until a reaction equilibrium is attained. In a heterogeneous metathesis catalyst a catalytically active metal compound is attached to the surface of a fixed support, so that the catalyst can readily be separated from the reaction mixture.
Besides the support and the catalytically active metal compound, known heterogeneous metathesis catalysts often contain promoters to improve the activity of the catalyst. Activity here and hereinafter is understood to be the weight of the converted olefins per unit weight of catalyst 5 minutes after the start of the reaction.
EP-A-152,112 discloses such a heterogeneous metathesis catalyst consisting of a tungsten oxide on a silica support containing a titanium-containing compound as promoter to increase the activity of the catalyst.
Drawbacks of the known heterogeneous metathesis catalyst are the low activity and the very high temperature at which the catalyst is only active (300-500.degree. C.).